DATING GLACIAL FEATURES IN NEW YORK'S LOWER HUDSON VALLEY – THE LAST DEGLACIATION OF THE EASTERN LAURENTIDE ICE SHEET

The Laurentide Ice Sheet (LIS) was the Earth's dominant continental ice sheet during the Last Glacial Maximum (LGM). The LIS deglaciation represents a dramatic environmental change and released enormous amounts of fresh water to the Atlantic Ocean, potentially slowing down the North Atlantic Deep Water formation and, in turn, ocean thermohaline circulation which affects global climate. To evaluate the impact of this fresh-water signal, it is important to know the timing and rate of retreat of the LIS at the end of the LGM, particularly along the Eastern margin of the United States.

Moraines and other glacial features in New York provide evidence of the advance and retreat of the Eastern LIS. Preliminary ¹⁰Be surface exposure ages from boulders on the LIS terminal Harbor Hills moraine on Long Island indicate that substantial LIS retreat began between 17 and 20 ky ago. ¹⁰Be ages of ice-recessional features in Manhattan's Central Park and in the Hudson Valley region (Black Rock Forest and Harriman State Park) reveal dates indistinguishable from those on Long Island, indicating relatively rapid initial ice sheet recession during the last termination.

We present new ¹⁰Be ages from the LIS terminal moraines in Long Island (Harbor Hills and Ronkonkoma moraines) and in Staten Island, as well as from recessional stages in Hudson Valley to further refine the chronology of the Eastern Laurentide Ice Sheet at the end of the Last Glacial Maximum. ¹⁰Be exposure ages are compared to existing radiocarbon chronologies as well as to previously published ¹⁰Be ages from moraines in New England.